MADISON, Wis. (AP) -- A decade ago, foresters feared an invasive Chinese beetle would spell doom for American ash trees. But a counterpunch emerged in the form of a powerful pesticide that can not only save infested trees but inoculate them against the emerald ash borer.

Milwaukee has been using the chemical for four years without losing one tree to the bug, but the pesticide must be reapplied every few years, creating a quandary for cash-conscious city councils.

Municipal officials on the edges of the ash borer's ever-expanding range face a choice: Cut down their ash trees and replace them with other species - a large one-time expense - or commit to spending lesser sums on pesticide treatments, perhaps for years. Their decisions can affect everything from property values to storm water retention.

"There's no reason for a landscape tree to die now if someone is willing to put some money into it," said Deb McCullough, a Michigan State University forest entomology professor who helped test the pesticide before it went on the market. "(But) some cities have a tough time allocating money from a municipal budget to protect trees when they're trying to keep firemen and policemen on the job."

The emerald ash borer's larvae kill ash trees by consuming the trees' nutrient transport tissues. The beetle has spread to 21 states as well as Quebec and Ontario since it was discovered near Detroit in 2002, leaving tens of millions of dead trees in its wake.

In the early years of the infestation, most cities with the pest dealt with it by cutting down all their ash trees, even healthy ones. Municipal leaders feared the beetle would kill so many trees so quickly that cutting crews wouldn't be able to remove the husks before they toppled and caused damage.

The game shifted in 2008, though, when federal regulators approved a pesticide called TREE-age for use against the beetle. A 2009 report from the North Central Integrated Pest Management Center, a network of researchers that advises the federal government on pest control, said the pesticide can save infested trees if applied early enough, as well as inoculate trees against the beetle for at least two years. Other ash borer pesticides have to be applied annually and have produced inconsistent results, according to the report.

Milwaukee and Chicago have been using the pesticide since 2009, committing millions of dollars to the effort over the years.

Officials in both cities said treatment allows them to replace ash trees with other species on their own schedule and said the approach is cheaper than taking down all the trees at once. Milwaukee, for example, spends about $950,000 a year on treatment versus the $27 million it would have cost to remove the city's 33,000 street ash trees. Meanwhile, residents continue enjoying the trees' benefits, such as shade, sucking up storm water runoff and boosting property values.

"We're totally in the driver's seat, which is the envy of most communities that have (the ash borer)," David Sivyer, the city's forestry services manager, said.

City officials in Madison, where the bug was confirmed in November, have implemented a hybrid plan that calls for cutting down trees in poor condition and treating larger trees. That decision is expected to cost as much as $1.1 million dollars annually by 2019.

About 150 cities and towns are currently using the pesticide, said Leah Hancock, product marketing manager for Arborjet, which produces TREE-age. But others are wary of committing dollars over the long term.

City officials in Minneapolis, where the beetle was discovered in 2010, have proposed a plan calling for a new $1.1 million tax levy every year for eight years to remove 40,000 ash trees and replanting different species. The city's park board in December approved the first year of the levy.

Foresters discovered the emerald ash borer in Boulder, Colo., in September, marking the bug's farthest progress west. City Forester Kathleen Alexander said Boulder is trying to determine the extent of the infestation. Then the city will have to make some hard decisions about whether to treat trees, remove them or both, she said.

City leaders in La Crosse have been grappling with the beetle since 2012. They've decided to pull out their 6,000 public ash trees and replant new species. They anticipate the effort will cost about $2 million over four years. That compares with an estimated $1.8 million to treat all 6,000 trees over six years, said Cinthia Johnson, the city's parks and forestry coordinator.

"EAB is going to be in our community longer than six years," she said. "You're looking at another six years and another six years. With the removal and replacement over four years, we're done."

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